The present invention relates generally to medical injectors and syringes used therewith and, more particularly, to pressure control systems for injectors.
A number of powered injectors and injector-actuated syringes for use in medical procedures such as angiography, computed tomography (CT), ultrasound and magnetic resonance imaging (MRI) have been developed. For example, U.S. Pat. No. 4,006,736 discloses an apparatus for injecting fluid into the vascular system of a human being or an animal. Likewise, U.S. Pat. No. 4,677,980 discloses an angiographic injector including a rotating turret for housing two angiographic syringes in readiness for injection. Furthermore, U.S. Pat. No. 5,383,858 discloses a front-loading injector and a syringe mountable thereon for injection procedures. The disclosures and drawings of U.S. Pat. Nos. 4,006,736, 4,677,980 and 5,383,858 are hereby incorporated by reference.
Syringe-based injection systems are susceptible to maximum pressures that are higher than the desired programmed pressure when the fluid delivery path is closed or becomes blocked during an injection procedure. Fluid delivery paths can become closed or blocked for any number of reasons, including a closed stopcock or kinked tubing along the fluid path.
The programmed maximum pressure may be exceeded in the syringe due to the rapid rise of the fluid pressure in closed or blocked fluid delivery paths. In normal, open fluid path injection procedures, the control systems of conventional injectors are able to detect when the programmed maximum pressure is achieved and take control steps to decrease the injection speed to prevent pressure overshoots. However, the control systems are unable to deactivate or reverse the injector motor without inducing large and undesirable pressure fluctuations in the syringe and associated disposables. Therefore, during a normal injection, the control systems slow the injection as much as possible by terminating the current to the motor at a rapid controlled rate, thereby avoiding the large pressure fluctuations.
Unfortunately, these conventional control systems are unable to manage the problem of higher maximum pressures experienced during a closed or blocked fluid path injection.
In addition, powered injectors typically need to accommodate syringes having varying stiffness properties. For example, powered injectors may use both plastic and glass syringes, while utilizing the same pressure control algorithm.
The present invention provides pressure control systems that control pressure overshoots in injector-actuated syringes and associated disposables caused by, for example, closed or blocked fluid delivery paths.
Further, the present invention provides pressure control systems for injectors that accommodate syringes having different stiffness properties, such as plastic and glass syringes.
According to a first aspect of the present invention, a pressure control system lowers pressure overshoots in syringes and associated disposables during an inadvertent closed or blocked fluid path injection.
According to a second aspect of the present invention, a pressure control system allows an injector to accommodate syringes having varying stiffness properties, while not increasing pressure overshoots during closed or blocked fluid path injections. For example, the pressure control system allows an injector to accommodate both plastic and glass syringes, while utilizing the same pressure control algorithm.
According to a third aspect of the present invention, a pressure control system correlates stiffness characteristics of one configuration of syringe to those of a different syringe. Therefore, the pressure control system is able to accurately control pressure overshoots incurred during an inadvertent closed fluid path injection on all suitable syringe types.
In one embodiment, the pressure control system comprises a compliant injector piston that engages a plunger on an injector-actuated syringe.
In another embodiment, the pressure control system comprises a compliant piston extension member that is connected to a conventional injector piston and a plunger on an injector-actuated syringe.
The present invention, along with further aspects and attendant advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.